PalindromeTree.cpp

Palindromic-Tree/PalindromeTree.cpp

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+#include <iostream>
+#include <cstring>
+
+using namespace std;
+
+const int MAXN = 105000;
+
+struct node {
+    int next[26];
+    int len;
+    int a;
+    int num;
+};
+
+int len;
+char s[MAXN];
+node tree[MAXN]; 
+int num;            
+int b;           
+long long ans;
+
+bool addLetter(int pos) {
+    int cur = b, curlen = 0;
+    int let = s[pos] - 'a';
+
+    while (true) {
+        curlen = tree[cur].len;
+        if (pos - 1 - curlen >= 0 && s[pos - 1 - curlen] == s[pos])     
+            break;  
+        cur = tree[cur].a;
+    }       
+    if (tree[cur].next[let]) {  
+        b = tree[cur].next[let];
+        return false;
+    }
+
+    num++;
+    b = num;
+    tree[num].len = tree[cur].len + 2;
+    tree[cur].next[let] = num;
+
+    if (tree[num].len == 1) {
+        tree[num].a = 2;
+        tree[num].num = 1;
+        return true;
+    }
+
+    while (true) {
+        cur = tree[cur].a;
+        curlen = tree[cur].len;
+        if (pos - 1 - curlen >= 0 && s[pos - 1 - curlen] == s[pos]) {
+            tree[num].a = tree[cur].next[let];
+            break;
+        }       
+    }           
+
+    tree[num].num = 1 + tree[tree[num].a].num;
+
+    return true;
+}
+
+void initTree() {
+    num = 2; b = 2;
+    tree[1].len = -1; tree[1].a = 1;
+    tree[2].len = 0; tree[2].a = 1;
+}
+
+int main() {
+
+
+    gets(s);
+    len = strlen(s);
+
+    initTree();
+
+    for (int i = 0; i < len; i++) {
+        addLetter(i);
+        ans += tree[b].num;
+    }
+
+    cout << ans << endl;
+
+    return 0;
+}